Sound of silence

Medical ultrasonics, first introduced for diagnosis, are also found in other applications

By Morand Fachot

Ultrasounds, which cannot be heard by humans, are used extensively in healthcare. They are found in diagnosis, surgical, therapeutic and cleaning environments, as well as in other medical and dental applications. The IEC has been involved in preparing International Standards for ultrasonic medical (and other) equipment since the mid-1950s.

Abdominal ultrasound used to search for gallstones (Source: Life Science Facts)

Diagnosis

Early trials to use sounds to detect objects were prompted by the need to track hostile submarines during WW 1 (World War 1).

Research into the possible use of ultrasonics for medical diagnosis started after WW 2.

Ultrasonic scanning, or ultrasonography, using high frequency sound waves to produce images, viewed on a screen, of internal organs, vessels and tissues, is arguably the best known of all ultrasonic medical applications. This is due largely to the widespread use of prenatal ultrasound scans, also known as echographs, which show images of a fœtus in the mother's womb.

Ultrasonic scans are quicker and easier (and less costly) to use than CT (computerised tomography) scans and MRI (magnetic resonance imaging) and are therefore frequently used to monitor and diagnose the condition of certain organs, such as liver, kidneys or gallbladder. Echocardiograms, or ultrasonic scans of the heart, are also used to diagnose and follow up heart conditions.

Silent knife

Surgery is another area that makes increasing use of ultrasound technology. USIs (ultrasonic surgical instruments) convert an ultrasonic signal into a mechanical vibration using a transducer; a waveguide then amplifies and propagates the vibration. USIs have been found to be very useful in a variety of medical procedures as they can cut bone and other tissue while simultaneously coagulating the tissue to reduce bleeding. Their use generally reduces the average length of surgery and of damage to tissue, resulting in fewer complications overall.

Non-invasive therapeutic applications

Ultrasound energy, in the form of non- or minimally-invasive HIFU (high-intensity focused ultrasound), also known as HITU (high-intensity therapeutic ultrasound), is used for tissue ablation in the treatment of cancers and conditions such as BPH (benign prostatic hyperplasia) by applying ultrasound energy to heat and destroy diseased tissues.

In addition, HIFU/HITU ultrasonic methods are applied to other treatments.

The area that has benefited most from the technology is ESWL (extracorporeal shock wave lithotripsy). This uses ultrasound pulses to smash kidney, gallbladder or liver stones using non-invasive intervention. Stones are located and targeted using an ultrasound (or other) imaging system. They are then broken up into smaller pieces that are subsequently evacuated naturally through urination. ESWL was introduced in the early 1980s and quickly replaced surgery as the most widespread treatment for stones. However, non-invasive does not mean totally risk-free: ESWL may also result in certain complications.

HIFU/HITU may also be used for thrombolysis, the breakdown of blood clots in vessels, although this is currently mainly carried out with drugs. The use of "ultrasound patches" to heal venous ulcers, accelerate healing and treat chronic wounds is also being tested.

Enhanced bone healing and physiotherapy are other domains that have benefited from ultrasonic technology, using lower intensity ultrasounds. In physiotherapy, ultrasounds are applied to the skin, using a gel to ease the transmission of ultrasound to soft tissues to reduce pain and inflammation resulting from rheumatism, tendinitis, joint injuries, etc.

So-called phacoemulsification, in which an ultrasonic instrument is employed in ophthalmology for cataract surgery, is another application.

Ultrasounds are also being used to enhance drug distribution to treat tumours, in the brain in particular, where such distribution may be particularly difficult to achieve. Ultrasound therapy can be found in cosmetic applications, in particular in so-called non-invasive liposuction in which ultrasounds are used to melt and liquefy body fat without having to resort to surgery. It is also used in skin treatment, where its deep-tissue micro-massage effect is reported to improve skin tone, softness, and texture. Cosmetic practitioners claim that ultrasound therapy can be used to reduce stretch marks, wrinkles, scars and sun-based damage that has been caused to skin.

Dental care

One public health application of ultrasonics that is widely known is the use of descalers in dental practice to remove plaque, which, if left, will harden into tartar. Ultrasonic descalers have a tip that vibrates at high frequency to break down the bacterial matter to which plaque and calculus stick. Even if hand descalers are also used sometimes to finish the cleaning, the procedure is then smoother and less painful.

Keeping patients safe and infections at bay

All medical and dental equipment must be kept absolutely clean before use and in particular in case of contact with a patient's sterile tissue (surgical instruments) or mucous membranes (endoscope). Failure to do this can result in the introduction of pathogenic microbes that can lead to infection.

Therefore, it is essential to clean, disinfect and sterilize (in that order) all multiple-use instruments and devices after they have been used on a patient or in an operation. Ultrasonic cleaning is particularly efficient for the physical removal of organic waste on equipment or devices that have joints, crevices or other areas that are difficult to clean. Ultrasonic cleaners use a special washing solution. Ultrasonic cleaners are also deployed in industrial applications.

International Standards for ultrasonics? What's the point?

Medical diagnostic ultrasonic equipment has been around for a long time and is expanding more rapidly than any other imaging process. Surgical and therapeutic ultrasound applications have also experienced a significant and continuous growth over the last decade, a trend that is expected to continue, in particular for HIFU/HITU applied to certain surgical procedures. Ultrasonic cleaners complete the loop in terms of ultrasonic applications in the medical environment, which now range from diagnosis to surgical and non-invasive treatments.

The need to characterise the ultrasonic fields and to establish a means for determining exposure levels to them is a recognised requirement for meeting regulations worldwide. To achieve this, International Standards are needed.

IEC TC (Technical Committee) 87: Ultrasonics, prepares International Standards related to the characteristics, methods of measurement, safety and specifications of fields, equipment and systems in the domain of ultrasonics. Its work covers not only medical equipment, but also industrial applications. IEC standardization work started within a Working Group of TC 29: Electroacoustics, in 1955. Given the wide scope of the work, a full Technical Committee, TC 87: Ultrasonics, was created in 1985.

As of April 2014, TC 87 had published 44 International Standards, Technical Reports and Specifications, and is continuing to develop more, the majority concerning medical applications.

Gallery

Abdominal ultrasound used to search for gallstones (Source: Life Science Facts)

COPYRIGHT

AVAILABLE FOR DOWNLOAD

ABOUT THE IEC

The IEC (International Electrotechnical Commission) is the world’s leading organization that prepares and publishes International Standards for all electrical, electronic and related technologies. Close to 20 000 experts from industry, commerce, government, test and research labs, academia and consumer groups participate in IEC Standardization work.